It is known to produce nonwoven webs by so-called “melt-blowing” processes from various synthetic polymers.
It is, furthermore, known to produce nonwoven webs made by a melt-blowing process employing a cellulose solution in N-methyl-morpholine-N-oxide (“NMMO”) from, inter alia, WO 98/26122, WO 99/47733, WO 98/07911, U.S. Pat. No. 6,197,230, WO 99/64649, WO 05/106085 and EP 1 358 369. Such products are also generally mentioned in DE 101 40 772 A1 and in WO 2007/000319 A1.
The melt-blowing processes disclosed in the above-referenced documents are characterized in that extruded threads of the cellulose solution in NMMO are picked up by a gas stream flowing in a generally parallel direction to the path of the filaments. The cellulose solution, which is ejected through the orifices, is formed to liquid strands or latent filaments, which are drawn (or significantly decreased in diameter and increased in length and may be split into several sub-filaments) by the gas stream.
The filaments are then collected, for example on a rotating drum, whereby a web is formed.
In the following, this process is referred to as “Lyocell melt-blowing process”. Nonwoven melt-blown webs made by the Lyocell melt-blowing process will in the following be referred to as “Lyocell melt-blown webs”. For the purposes of the present invention, the term “Lyocell melt-blowing process” encompasses both processes by which endless filaments are obtained (such processes also referred to in the literature as “spunbonding processes”), processes by which fibers of a discrete length are obtained and processes by which mixtures of endless filaments and fibers of discrete length are obtained.
In contrast thereto, WO 06/035458 discloses a process for the production of so-called “spunlaid nonwovens”, i.e. the extruded filaments are not stretched by a gas stream, but by the flow of the precipitation fluid.
Various means of bonding nonwoven webs are known nowadays. These means, depending on the nature of the nonwoven web employed, comprise chemical bonding, thermal bonding, needle-bonding and bonding via hydroentanglement.